Modifying and improving: "OM651 Modifications"

How to modify and upgrade the Mercedes OM651

"Comprehensive guide to tuning the Mercedes OM651 engine!"

Sites like TorqueCars often are getting messages about how to improve the OM651 from people inquiring about getting more power from the OM651 and wanting to know what are the best OM651 mods that work. So let us look into Mercedes OM651 mods and outline the best modifications on this great engine and point out some potential pitfalls along the way.

Car Tuning Tips will detail the best approach to OM651 tuning and provide tips on the optimum modifications for your car. Mercedes OM651 provide a fun base for your project and with a few sensible uprated mods like ECU maps, turbo upgrades and camshafts you will greatly maximise your driving fun.

When talking about the ultimate parts for your OM651 engine, we are going to concentrate on the parts that give the biggest return for your cash.

Improving air intake on the OM651

You need air matched to fuel for an engine to work. If there is little supply of fuel then it will run lean, if there is not enough air it runs rich sapping power . We'll pick up on fuelling later in this article but for now we shall look at air supply.

So Forcing air and fuel into your OM651 is the whole point to any engine performance tuning project.

It is common that there is a limitation in the air flow sensor MAP/MAF/AFM on the OM651 when a lot more air is being sucked into the engine.

We note 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited power at a much lower level.

Intake manifolds flow the on the suck phase from the filter and allow it to be fed into the engine and mixed with fuel.

Design and flow rate of the Plenum can make a noticeable difference to to fuel delivery on the OM651.

Commonly we find the air intake manifolds are needing performance upgrades, although some makers provide reasonably well designed air intake manifolds.

Increasing the OM651 valve size, doing a bit of 3 or 5 angle valve jobs and porting and head flowing will also boost bhp, & importantly will make space for a greater bhp increase on other parts.

OM651 performance cam tips.

Some OM651 engines respond better to mild camshaft durations so set your engine up on a rolling road.

The ecu map and injectors and fuel pump also will make differences on the power gains you'll hit.

Altering valve durations can alter the power band and on most engines the exhaust and intake durations do not need to match, although most cams and tuners use matched pairs there are some advantages to extending the intake or exhaust durations.

Significant air intake, and exhaust improvements on the OM651 can be made from camshaft upgrades. Changing the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the bhp and power output.

NB: Fast road cams tend to bump the power through the rev band, you may sacrifice a little bottom end bhp but high end rpm power will be higher.

Race cams, bump the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

For a car driven daily you should ideally to optimize your power band to your usage of the car.

I'd be gobsmaked if you find a OM651 Race camshaft is a pleasure to live with when driving in heavy traffic.

Stage 1, 2 and 3 mods for the OM651

Before we break the best tuning upgrades down into stages of tune, let's list the most effective tuning upgrades for you.

1. Suspension Upgrades - always improve your cars handling
2. Brake Upgrades - Even before adding power improve those brakes
3. Intake - make sure the intake is not restricted, use filters and intake upgrades to improve this
4. Exhaust - as with 3 ensure there is not restriction in the exhaust, cats are the usual bottleneck
5. Tunes - remapping, piggyback ECU's and aftermarket ECU's can all make decent gains
6. Fuelling - when you've increased power you'll need to match this with more fuel
7. Turbo upgrades - Improving the intake with a large turbo and better flowing intercooler will be the biggest power gain you'll see (but one of the most complex).

This video guide to tuning cars is a great starting point to work from in your project.

Stage 1 OM651 parts:

Panel air filters, Remaps/piggy back ECU, Drilled & smoothed airbox, Fast road camshaft, Sports exhaust manifold, Intake headers.

Stage 2 OM651 parts:

Fast road cam, Sports catalyst & performance exhaust, fuel pump upgrades, Ported and polished head, induction kit, high flow fuel injectors.

Stage 3 OM651 parts:

Internal engine upgrades (head flowing porting/bigger valves), Engine balancing & blueprinting, Adding or Upgrading forced induction (turbo/supercharger), Crank and Piston upgrades to alter compression, Twin charging conversions, Competition cam.

ECU flashing should help to to establish the full potential of all the parts you've done to your OM651.

You will typically expect to see gains of approximately 20-30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but your mileage may vary depending on the parts you've done and the condition of your engine.

Turbo modifications on the OM651

To get a turbo working on a NASP engine there is a lot involved, from lowering compression ratio to improved fuel supply and mapping, so we have found a great guide to helpavoid the common pitfalls or end up with an unfinished project because you were not told what you were getting into by doing this on the OM651.

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes excellent power gains.

When a car has a turbocharger modifications are going to make more power and we find turbocharged engines are made with uprated components.

However most engines have weakspots

See where you'll find these restrictions and upgrade to better quality crank and pistons to cope with the power.

There are many drivers spending a lot of money on turbo upgrades on the OM651 only to see the whole thing go up in smoke on it's first outing after it's used in anger.

Larger capacity turbo chargers tend to suffer a bottom end lag, and little turbo chargers spool up more quickly but don't have the peak rpm power band gains.

Thankfully the world of turbo units is always improving and we commonly find variable vane turbo units, allowing the vane angle is altered according to speed to lower lag and increase top end performance.

Twin scroll turbo units divert the exhaust flow into a couple of channels and push these at differently profiled vanes in the turbo. They also help the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large performance gains, although harder to install. We have this article on twincharging if you want to read more.

Tips about fuel supply on the OM651

Don't omit to increase the fuel delivery when you are increasing the bhp and torque - it makes the car more thirsty. It is important to be generous with your injector capacity.

The rule of thumb is to add 15% to the flow rate when buying an injector, this allows for injector deterioration and provides a little spare capacity should the engine require more fuel.

Don't forget that different fuel grades will usually require different settings, a high octane fuel will burn more efficiently than lower octane fuel for example. A car will trim fuel supply to keep within the ideal air fuel mix but at the extreme ends you may need to adjust your injector capacity, or the mapping or you'll get flat spots and potential lean or rich fuel issues..

Recommended OM651 performance exhaust upgrades

The only time you should look to increase your exhaust system with an upgraded one is if your current exhaust is actually causing a flow problem.

On most factory exhausts you'll see your flow rate is ok even on modest power gains, but on a serious tuning project with a big boost in power you will certainly need to get a better flowing exhaust.

Do not go with the largest exhaust you can find you'll slow the exhaust rate - the best exhausts for power gains are usually between one and a half to two and half inches. Your exhaust design, the bend angles and construction are what have more effect on flow rates than your pipe width to a certain extent. So the exhaust design is a big factor.

Usual exhaust restrictions are in the catalysts installed, so adding a higher flowing sports alternative will help avoid this restriction.

Decat pipes (NB:catalysts reduce harmful engine emissions) is illegal in most countries and regions.

Faults issues and things to look out for on the OM651

Like most engines an OM651, should have few issues if it gets properly serviced and looked after.

We cannot stress enough the need for oil changes with the correct grade of oil on the OM651, failure to do this will exacerbate engine wear, on a tuned OM651 this is more important than ever and close attention should be paid to your maintenance schedule.

If you are interested in learning more or getting impartial tuning advice for your OM651 why not pop over to the forums at TorqueCars where you can chat about OM651 tuning options and read about others projects who may be planning to do similar modifications on their OM651.

We need your help to complete and improve this page, so do give us your feedback in the comments box below.

We want to know your experiences with tuning parts on your OM651, it helps us improve our tips and keeps us current so please use the comments box to drop a tip.

This entry was posted under Makes and Models. Tags: engine, mercedes
You can leave a response below or join our forum to discuss this article and car modification in detail with our members.

If you liked this page please share it with your friends, drop a link to it in your favourite forum or use the bookmarking options to save it to your social media profile.

Check out TorqueCars new YouTube channel, and see their awesome new content...